The present invention relates to a mold-releasable curable organopolysiloxane composition or, more particularly, to a curable organopolysiloxane composition suitable as a material of a matrix mold having good mold-releasability for the preparation of replicas from an epoxy resin, urethane resin, plaster of paris and the like by casting into the matrix.
It is a well established technology to prepare replicas by using a matrix mold made from a cured silicon rubber into which a curable liquid resin such as epoxy resins, urethane resins and the like is cast and cured therein into a replica body. A great variety of parts in automobiles, electric appliances and others are fabricated by this technique and are under practical use. As a trend in recent years, these casting-prepared resin parts are required to be more and more upgraded in respect of performance as well as in appearance. In this regard, improvements are now under way in the properties of the casting resin while the improvements in the properties of the casting resin per se are sometimes accompanied by an adverse influence on the surface of the silicone rubber-made matrix mold greatly decreasing the durability of the mold or the number of replica pieces prepared by using a single matrix mold to cause an economical disadvantage.
With an object to improve the durability of a silicone rubber-made matrix mold used in resin casting, it is practiced that the finely divided reinforcing silica filler before compounding in the silicone rubber composition is rendered hydrophobic by the surface treatment with an organosilazane compound such as hexamethyl disilazane, octamethyl trisilazane, 1,5-di(3,3,3-trifluoropropyl)-1,1,3,3,5,5-hexamethyl trisilazane and the like. It is also known that silicone rubber-made matrix molds can be imparted with an improved tear strength when the hydrophobic treatment of the reinforcing silica filler is performed with a mixture of the above mentioned organosilazane compound and a vinyl-containing organosilazane compound such as 1,3-divinyl-1,1,3,3-tetramethyl disilazane, 3-vinyl-1,1,1,3,5,5,5-heptamethyl trisilazane, tris(trimethylsilylamino) vinyl silane, vinyl-containing poly(dimethylsilazane) and the like or the hydrophobic reinforcing silica filler is further treated with these vinyl-containing organosilazane compound.
The above mentioned method by the surface treatment of the reinforcing silica filler is indeed effective at least to some extent for increasing the durability in the mold releasability of silicone rubber-made matrix molds but is still not quite satisfactory in respect of the mold releasability with durability when the casting resin is a high-performance urethane resin or epoxy resin as in the major current of the modern resin casting technology.